Specific Aims: Research Project 2 tests the hypotheses that polybrominated diphenyl ethers (PBDEs), perfluorinated chemicals (PFCs) and environmental organic acids (EOAs) accumulate differently in human fetuses than in pregnant women during mid-gestation, and that these chemical exposures negatively impact placental development and function, important outcomes that can adversely affect in utero growth and development. Accordingly, the goal is to compare 2nd trimester maternal serum, placenta and fetal liver levels of PBDEs, PFCs and select EOAs through traditional and novel biomonitoring approaches (Aim 1); and evaluate the relationship between these chemical exposures and disruptions of placental development by analyzing morphological and molecular markers of trophoblast differentiation and function (Aim 2).